A couple of years ago I received a paper to review in which the authors detailed how they had invented a new trap for sampling and collecting beetles in tropical forests. I was astounded to see that they were describing a window pane trap, something that I had known about since I was a student and which has been used by entomologists worldwide for many years. I quite politely pointed this out in my review and directed the authors to Southwood ‘s Ecological Methods (1966). The other referee was less tolerant, her/his report simply read “see Southwood page 193”. At the time I wrote the review it was firmly stuck in my mind that the technique was as old as the hills, or at least as old the invention of cucumber frames 🙂 I certainly thought of it as a Victorian or Edwardian invention. To my surprise when I started delving into the literature all the Victorian references to window traps turned out to be ways to protect households from invasion from houseflies and other unwanted flying insects; nothing to do with entomological sampling or collecting. E.g. this patent from 1856 where the inventor describes its operation as follows “The flies enter the trap through the passage B, as illustrated, and after satisfying their wants from the baitboard seek to escape, and being attracted by strong light from the glass back they fly in that direction and being headed out crawl up the glass back until they nearly reach the upper edge of the same, when, being still attracted and deluded by light from the glass top, they attempt to fly upward or through the same and in doing so instead of rising, are, owing to the inclination of the glass top, precipitated into the trough of soap suds and drowned, as illustrated in the drawing.

This fly trap is exceedingly simple, quite cheap, and only costs about twenty-five cents, and has been tried and found to answer well the purpose intended.”

Unfortunately not what I was looking for 🙂

Despite scouring Google and Google Scholar, to the lengths of even getting to page 30, which apparently no-one does, it seems that the earliest reference to what we think of as a Window (pane) trap was not invented until 1954 (Chapman & Kinghorn, 1955) to sample Ambrosia beetles (Trypodendron spp.) and other scolytids in Canadian forests. There is unfortunately no picture to illustrate the trap, but the written description is fairly clear “ a piece of window glass (2 X 2 ft) set in a three-sided wooden frame from which a sheet metal trough is hung. The trough is filled with fuel oil or water….Traps are hung from various types of pole framework depending on their location, and guy wires are used to keep them from swinging.” I am pretty certain that this 1954 date is the earliest record as even that vade mecum of the entomologist, Instructions for Collectors No. 4a (Smart, 1949) has no mention of it.

The theory behind the window (pane) trap is that flying insects are unable to see the clear glass (or Perspex), bang into it, and stunned, fall into the collecting trough where they drown to be collected and identified later. A fantastically simple idea, which is why I was surprised that it took entomologists so long to invent it. As far as I can tell from the written description given by Chapman & Kinghorn (1955), the trap was suspended from a ground based framework. I think that this version I found in Chapman (1962) is probably the original design or at least very close to it.

Despite its efficiency the ‘classic’ windowpane trap has perhaps not been used as much as it deserves, instead, a plethora of alternative designs have been described since the mid-1970s. So for example we have a small-scale tree hanging version, with a four-way window being used to catch forest coleoptera (Hines & Heikkenen, 1977). Although the small area flight intercept traps were

The Hines & Heikkenen (1977) small area window flight intercept trap.

relatively easy to deploy, they obviously just weren’t big enough for some people. In 1980, Peck & Davies, described a large-area window trap used to catch small beetles. This used the central panel of a Malaise trap as the window under which they placed a large metal collecting trough. Unlike the Hines & Heikkenen trap, this like the original Chapman & Kinghorn trap, was ground-based. The

The Peck & Davies(1980) large-area “window” trap.

authors, in an attempt to impose order on to the entomological collecting world, urge other coleopterists to adopt a similar trap design. In 1981 we see a modification to the Hines & Heikkenen

The Omnidirectional flight trap (Wilkening et al., 1981).

trap to improve its efficiency (Wilkening et al., 1981). Despite the name omnidirectional, implying that it catches insects from all directions, this trap catches large fast-flying insects in the lower chamber, into which they fall stunned on bumping into the window pane and slow upwards flying insects in the upper chamber. The authors argue that the original version of the trap did not catch slow-flying insects as they were able to detect the pane early enough to avoid being stunned and then took evasive action by flying up and away from the collecting bottle. The new improved version takes advantage of this behaviour and traps them in the upper bottle into which they inadvertently fly.

In 1988, my fellow editor, Yves Basset, then at Griffiths University in Australia, now at the Smithsonian Tropical Research Institute in Panama, decided to combine a Malaise trap with a Hines & Heikkenen trap to produce what he called a composite interception trap (Basset, 1988),

Despite this ingenious trap, trapping forest canopy insects obviously continued to occupy the minds of forest entomologists and in 1997 another pair of entomologists working in Australia came up with yet another design for a flight intercept trap, this time one that could be suspended at different heights in the canopy and left for long periods of time (Hill & Cermak, 1997). The novelty of this trap

The Hill & Cermak modified Window trap

as far as I can make out is the use of multiple collecting chambers (ice cream tubs) and a plastic instead of a Perspex, ‘window’.

Entomologists are forever tinkering and ‘improving’ with sampling methods, so it should not be a surprise to find a group of entomologsist from the USA describing the ultimate in a composite trap, this time a combination of four different traps, the cone, the Malaise, the yellow pan trap and the flight intercept trap (Russo et al., 2011). Interestingly, the authors describe this as a passive trap,

concluded that their model was more efficient and “should be used as an alternative and standardised method for future empirical studies” a bold statement indeed, as they did not compare their trap with any of the other traditionally used window pane traps described above.

And finally and right up to date, and in the best entomological tradition of using cheap easily obtainable materials, yet another variant on the flight intercept trap; this time using plastic bottles – pop, soda, water, cider, beer, take your pick J (Steininger et al., 2015).

I am sure, however, that as I write, some ingenious entomologist out in the field somewhere, is thinking of yet another modification to the window (pane) flight intercept trap to make my post out of date!

Apropos of the ultimate composite trap, I came across this combination four-way window-yellow pan trap combination some years ago, but have not been able to find a published inventor of it. I should also add that flight intercept traps are also sometimes known as impact traps.

*Vade mecum, a handbook or guide that is kept constantly at hand for consultation.

For my M.Sc. I used a version of the window pane trap that replaced the window with tightly strung fishing line. The trap was used to catch Colorado potato beetles in flight over different types of crops in Atlantic Canada. I (and a few summer students) spent hours and hours weaving fishing line back and forth on a frame of nails to create each window pane. We would then have to mount these in special metal frames driven into the rows between the crop, and then slather the top and bottom of the frame with stickum. We did all this because Colorado potato beetle is remarkably perceptive in flight and could see the standard window pane trap. The fishing line was strung such that the distance between the strands was less than the wingspan of a beetle in flight (more or less) and so upon impacting the trap they would then stop flying and fall into the collecting trough at the bottom (or climb up or down into the stickum).

The downside of this design is that the fishing line was prone to snapping in strong winds (or even mild breezes), bird impacts, a tractor driving by, or for no apparent reason. When this would happen I would have to replace the trap, getting thoroughly tangled in fishing line and stickum in the process. The design was that of my M.Sc. supervisor Gilles Boiteau based on a modified version of an aphid trap (http://jee.oxfordjournals.org/content/93/3/630). He dubbed them ‘Harp traps’ (for obvious reasons). We even managed to publish a paper using the data from these traps (www.phytoprotection.ca/pdf/phytoprotection_84_133.pdf). but the whole experience put me of insect traps for a long, long time.

Welcome to the lounge, where entomologists and insect enthusiasts can relax, grab a cup and put on a nice music. Step out of your day job, and step into your zone, where you reconnect with your passion for insects and enrich yourself with more knowledge.